Ultrasound systems and methods for automated fetal heartbeat identification

ABSTRACT

Ultrasound systems and methods provide a workflow to automatically identify a fetal heartbeat. A region of interest (ROI) is identified in an ultrasound image and an ROI icon is positioned around or over a fetal pole and/or fetal heart. The ultrasound system produces spatially different M-mode lines associated with the ROI icon. The ultrasound system can identify a fetal heartbeat and estimate the fetal heart rate from echo signals received from echo signals associated with at least one of the spatially different M-mode lines. The echo signals for the M-mode lines can also be ranked according to the likely presence of a fetal heartbeat in the echo data.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application claims the benefit or priority of and describesrelationships between the following applications: this application is acontinuation of U.S. patent application Ser. No. 15/027,050, filed Apr.4, 2016, which is the National Stage of International Application No.PCT/IB2014/064575, filed Sep. 17, 2014 which claims the priority of U.S.Provisional application 61/886,694 filed Oct. 4, 2013, all of which areincorporated herein in whole by reference.

Ultrasound is well suited for fetal imaging because it performsnoninvasive imaging without exposing either the mother or the fetus toionizing radiation. An objective of many fetal examinations is to assessthe development of the fetal anatomy to determine whether the fetus isdeveloping normally. As ultrasound image quality has improved over theyears, more areas of the anatomy can be visualized for developmentalassessment and in greater detail. Consequently, fetal ultrasound examshave become more thorough with increased requirements for anatomy thatis to be assessed. One area of the anatomy that is greatly scrutinizedis the developing fetal heart.

Ultrasound systems can be used to detect a fetal heartbeat within aboutfive weeks of gestation. At this point, a normal fetal heart rate issimilar to the mother's, e.g., about 80-85 beats per minute. The heartrate will steadily increase at about three beats per minute per day overthe next month. After further development, a healthy fetal heart ratecan range between 120 to 200 beats per minute (BPM). Accordingly, anultrasound examination can be used to determine whether there is risk ofa miscarriage if the fetal heartbeat not within an acceptable range ofvalues. For example, a relationship between the fetal heart rate andrisk of miscarriage at 6-8 weeks of pregnancy indicates about a onehundred percent chance of miscarriage if the fetal heart rate is lessthan seventy beats per minute. The chances of miscarriage decrease inline with an increasing measured heart rate, e.g., if the heart rate isless than ninety beats per minute the chances of miscarriage are stillhigh at about an eighty-six percent chance of miscarriage.

In recent years the outflow tracts of the heart have become a focus ofattention for detecting and measuring fetal heart rates. The cardiacoutflow tracts of the fetal heart, however, can be difficult to imageand detect for a useful period of measurement time. One reason for thisis the small size of this fetal anatomy. Another reason is that it isdesirable to not simply view the anatomy, but also the dynamics of theflow characteristics through the outflow tracts over the full fetalheart cycle. A further reason is that the outflow tracts undergoconsiderable development as the fetus grows, and consequently can havevarying appearances and complexity depending on fetal age. The outflowtracts can thus be difficult to identify on the ultrasound display, andit can be even more difficult to acquire images in the properorientation for adequate detection and/or measurement of a fetalheartbeat.

Another problem is that the fetus frequently moves and may not remainstationary during the time needed for data acquisition. When the fetusmoves, the orientation of the desired image data relative to the probewill change, and the fetal heart may leave the field of view entirely,resulting in an absence of the desired anatomy from the acquired dataset. Also, fetal movement during the acquisition can limit the accuracyof the measurement of the fetal heart cycle. In addition, it can also bedifficult to distinguish the fetal heart rate from the mother's heartrate and/or other rhythmic background artifacts.

Thus, there is a need for improved systems and workflows for theclinician that makes ultrasound systems easier to use and more accuratefor identifying a fetal heartbeat and measuring a fetal heart rate.

The present invention relates to medical diagnostic systems and, inparticular, to ultrasonic diagnostic imaging systems for identifying afetal heartbeat and an associated heart rate.

In accordance with the principles of the present invention, a diagnosticultrasound system has a workflow and controls that facilitateidentifying a heartbeat (e.g., a fetal heartbeat) and an associatedheart rate. The workflow enables the clinician to set a region ofinterest (ROI) about the fetal pole and/or fetal heart and then identifya fetal heart beat and/or acquire a fetal heart rate. The ultrasoundsystem is automated to repetitively scan differently oriented M-modelines associated with the region of interest. The ultrasound system canidentify a fetal heartbeat and estimate the fetal heart rate from echosignals received along at least one of the M-mode lines. The echosignals from the M-mode lines can also be ranked, for example, toidentify the M-mode scan most likely to be indicative of a heartbeat inthe echo data.

In the drawings:

FIG. 1 illustrates in block diagram form an ultrasonic diagnosticimaging system constructed in accordance with the principles of thepresent invention.

FIG. 2 illustrates a workflow in accordance with the present inventionfor identifying and measuring a fetal heart rate.

FIG. 3 illustrates an M-mode image of the motion of the heart muscle.

FIG. 4 illustrates a display of an implementation of the presentinvention for identifying an ROI in the image including the fetal heartand overlaying spatially different M-mode lines for identifying andmeasuring a fetal heart rate.

FIG. 5 illustrates a technique for automatically identifying a fetalheart beat and measuring a fetal heart rate.

FIG. 6A illustrates another technique for automatically identifying afetal heart beat and measuring a fetal heart rate.

FIG. 6B illustrates a technique for measuring fetal heart beat signalsby synthesizing M-line data from B-mode echo signals.

The present invention provides systems and methods for identifying aheartbeat (e.g., a fetal heartbeat) and an associated heart rate. Thesystems and methods can be used, for example, to reduce scanning timesfor sonographers, increase diagnostic confidence and simplify workflowsfor scanning maternal patients.

In one embodiment, the present invention includes an ultrasonic imagingsystem for identifying a fetal pole or heart and/or the associated heartrate. The systems of the present invention include an ultrasound probe.A variety of probes can be used and can include an array transducer. Thesystems also include an image processor that processes echo data fromthe probe. The echo data can include echo signals obtained by a varietyof imaging modes such as B-mode or M-mode image acquisition. The systemsalso can transmit the echo data and/or display the echo data from theprobe for viewing. Image displays in the system are coupled to the imageprocessor and adapted to display an ultrasound image including a fetalheart. A graphics generator in the system responds to a user controlthat identifies an ROI in the ultrasound image. For example, the ROI canbe identified in the vicinity of a fetal pole or fetal heart in theultrasound image using an ROI icon. A user control in the system isfurther adapted to initiate generation of spatially different M-modelines associated with the region of interest. In one example, an ROI canbe identified in the ultrasound image by user manipulation of a graphicicon and spatially different M-mode lines (e.g., between two to fiftyM-mode line locations) can be displayed in relation to the ROI. Thesystem acquires echo data (e.g., M-mode and/or B-mode echo signals)repetitively from some or all of the spatially different M-mode lines.The echo data is analyzed by the system or transmitted for analysis toidentify whether a fetal heartbeat is discernible in the M-mode imageacquired from at least one of the M-mode line positions. Some, one ornone of the temporally acquired echo data corresponding to each of thespatially different M-mode lines may exhibit echo signals indicative ofthe fetal heartbeat. Furthermore, the acquired echo data can be rankedbased on fetal heart rates measured in the echo data of the M-mode linesthat registered a fetal heartbeat. In some embodiments, a maternalheartbeat and/or heart rate can be identified in place of or in additionto the fetal heartbeat.

Referring to FIG. 1, an ultrasound system 10 constructed in accordancewith the principles of the present invention is shown in block diagramform. The ultrasound system is configured by two subsystems, a front endacquisition subsystem 10A and a display subsystem 10B. An ultrasoundprobe is coupled to the acquisition subsystem which includes atwo-dimensional matrix array transducer 70 and a micro-beamformer 72.Linear or curved array transducers can also be used. In someembodiments, only one plane of the matrix array will be used for M-modeor B-mode image acquisition. The micro-beamformer contains circuitrywhich control the signals applied to groups of elements (“patches”) ofthe array transducer 70 and does some processing of the echo signalsreceived by elements of each group. Micro-beamforming in the probeadvantageously reduces the number of conductors in the cable between theprobe and the ultrasound system and is described, e.g., in U.S. Pat. No.5,997,479 (Savord et al.) and in U.S. Pat. No. 6,436,048 (Pesque), eachof which is incorporated by reference herein.

The probe is coupled to the acquisition subsystem 10A of the ultrasoundsystem. The acquisition subsystem includes a beamform controller 74which is responsive to a user control 36 and provides control signals tothe microbeamformer 72, instructing the probe as to the timing,frequency, direction and focusing of transmit beams. The beamformcontroller 74 controls the beamforming of echo signals received by theacquisition subsystem by its control of analog-to-digital (A/D)converters 18 and a beamformer 20. Echo signals received by the probeare amplified by preamplifier and TGC (time gain control) circuitry 16in the acquisition subsystem, and then digitized by the A/D converters18. The digitized echo signals can then be formed into fully steered andfocused beams by the beamformer 20. The echo signals are processed by asignal processor 22, which performs digital filtering and can alsoperform other signal processing such as harmonic separation, specklereduction, and other desired image signal processing.

The echo signals produced by the acquisition subsystem 10A are coupledto the display subsystem 10B, which processes the echo signals fordisplay in the desired image format. The echo signals are processed byan image line processor 24, which is capable of sampling the echosignals or assembling echoes of a given beam into complete line signals.For M-mode image acquisition, at least one of the line signals outputfrom the image line processor 24 can be directed to an M-mode processor30. The M-mode processor generates M-mode images that are stored in theimage memory 28 and displayed on display 38. For B-mode imageacquisition, the image lines for a 2D image are scan converted into thedesired image format by a scan converter 26 which performs R-thetaconversion as is known in the art. The 2D image is stored in the imagememory 28 and displayed on the display 38.

In some embodiments, the 2D image data from the scan converter is outputto an M-mode synthesizer 40, which can generate M-mode images from the2D image data. As discussed further below, echo signals from the B-modelines can be synthesized to generate echo data associated with an M-modeline of interest. The synthesized M-mode images from B-mode echo signalsare further output to the image memory 28 and displayed. The image inmemory can also be overlaid with graphics to be displayed with theimage, which are generated by a graphics generator 34 which isresponsive to the user control 36. The graphics generator 34 alsocommunicates with the M-mode processor 30 and/or the M-mode synthesizer40 to correlate the image location of an associated M-line with thenormal and/or synthesized M-mode echo data for the corresponding M-line.A heart rate synthesizer 34 also communicates with the M-mode processor30 and/or the M-mode synthesizer 40 to apply algorithms, such as imageanalysis and/or frequency analysis algorithms, to the normal and/orsynthesized M-mode echo data to calculate a fetal heart rate. The heartrate analyzer 34 can also rank the M-mode echo data according to thelikely presence of a heartbeat in the echo data.

The normal and/or synthesized M-mode echo data can be stored in theimage memory 28 for future access or it can be displayed in real-time.Stored echo data can be stored by way of previously acquired cine loopsof B-mode images that can later be processed to calculate a heart rateusing synthesized M-mode echo data. During real-time imaging, motioncompensation may be applied to track the overall motion of the fetus.Motion compensation is described, for example, in U.S. Pat. No.6,589,176, which is herein incorporated by reference.

The system can be designed for 1D, 2D, and/or 3D ultrasound imaging. Incertain embodiments, 2D imaging can be used to achieve high frame ratesfor image acquisition. Frame rates on the order of tens to hundreds offrames per second can be used to record echo signals from a fetalheartbeat. If real-time volumetric imaging is used, the displaysubsystem 10B includes a 3D image rendering processor 32 which receivesimage lines from the image line processor 24 for the rendering ofreal-time three dimensional images. The 3D images can be displayed aslive (real time) 3D images on the display 38 or coupled to the imagememory 28 for storage of the 3D data sets for later review anddiagnosis.

FIG. 2 is a flow chart showing the workflow 76 of an implementation ofthe present invention. This workflow 76 begins with a step 78 ofreceiving an image of a fetal heart. In one embodiment, the image orimages of the fetal heart can be acquired during a scanning procedureand, while scanning the fetus, the sonographer can identify an ROI asdescribed herein.

In another embodiment, a sonographer can acquire a plurality ofultrasound images including the fetal pole and/or fetal heart that canbe stored (e.g., in a cine loop) and reviewed after scanning. After thescan, the sonographer can identify the ROI based on the collectedimages.

In step 80, an ROI in the ultrasound image is identified. In someembodiments, the location in the anatomy from which temporally discreteecho signals are acquired can be set to a default image location such asthe center of an image displayed during scanning or in images in anacquired loop of images. Alternatively, a location in displayed oracquired images can be designated by the user by manipulation of acontrol of the user controls in the system as discussed below inconjunction with FIG. 4. For instance, the user can manipulate ajoystick, trackball, or other control of the user controls to locate anROI designation icon over a region of interest in an image containing afetal heart. In certain embodiments, the ROI in the image is identifiedon the display screen by an ROI icon as discussed below, which can bepositioned completely or partially around or over the fetal pole and/orfetal heart. A variety of ROI icons can be used. For example, the ROIicon may be square, circular, oval or rectangular shaped. The ROI iconsmay also be a simple point, an X, or a crosshair indicator. In someembodiments, the ROI can be identified by positioning a mouse cursorover the ROI of the image.

In step 82, a plurality of spatially different M-mode lines that areassociated with the region of interest are generated. The M-mode linescan be generated and visualized on the display or they can be invisiblewith only the ROI icon being shown in the display. The M-mode lines aregenerated in relation to the ROI icon and are spatially distributed overthe region of interest in a variety of ways. For example, if a circularROI icon is used, the M-mode lines can be positioned as lines spanning adiameter of the circle. Alternatively, parallel line patterns orcrosshatch patterns could be positioned within an ROI icon, such as acircle or a square. Generally, M-mode line patterns (e.g., random,radial, parallel, crosshatch, and/or honeycomb patterns) can be used forany shape or type of ROI icon. Preferably, the spatially distributedM-mode lines are automatically generated by a system of the presentinvention. Spatially different M-mode lines can also be generated asdirected by a user by drawing lines in the relation to the ROI icon. Thesystem can also select a specific number of spatially different M-modelines to be used. In some embodiments, the number of spatially differentM-mode lines ranges between 2 to 100, between 5 to 50, between 10 to 50,or between 10 to 40.

The workflow also includes step 84, which is acquiring echo dataassociated with the spatially different M-mode lines. In someembodiments, the echo data can be repetitively acquired during ascanning procedure by M-mode image acquisition from a plurality of thespatially different M-mode lines associated with the ROI. Alternatively,the echo data can include echo signals from B-mode image acquisition.Here, the M-mode synthesizer synthesizes the echo data for a selectedM-mode line by combining echo signals from B-mode image lines thatintersect a given M-mode line position. Synthesizing the echo dataassociated with a selected M-mode line can be conducted in real-timeduring scanning as described below with regards to FIG. 5. A similarprocess can be used to synthesize echo data from a plurality of B-modeimages that are stored and later analyzed.

In step 86, the echo data of an M-line image is analyzed to identify afetal heartbeat and/or measure the associated fetal heart rate. Asdescribed below, the techniques for doing this include detecting motionof the fetal heart through analysis of the temporal echo data for an Mline positioned through the fetal heart. As shown in step 88, theworkflow can optionally include a ranking step that preferentially ranksthe recorded echo data for identification of a fetal heart rate fromsome or all of the spatially different M-mode lines.

A method of the present invention is carried out using ultrasoundsystems as described herein. The ultrasound systems can operate toperform any of the following steps: receive an ultrasound imageincluding a fetal pole or heart, identify a region of interest (ROI) inthe ultrasound image, generate a plurality of spatially different M-modelines associated with the region of interest, acquire echo datacorresponding to the spatially different M-mode lines, and analyze theecho data to identify a fetal heartbeat associated with at least one ofthe spatially different M-mode lines.

As described herein, M-mode lines are generated and used to detectmotion of the fetal heart so as to identify a fetal heart and/or measurea fetal heart rate. FIG. 3 illustrates a technique for detecting motionusing M mode imaging with an M line positioned through the fetal heart.In particular, FIG. 3 shows an M mode image 46 produced by an M linepositioned such that it extends through the left ventricle (LV) of thefetal heart. When positioned in this manner, the M line will passthrough the myocardial wall 12 on one side of the fetal heart, throughthe chamber of the LV, and through the myocardial tissue 14 on the otherside of the heart. An ultrasound beam is transmitted along this M linedirection through the LV periodically, and the received A-line from eachtransmission is shown on the display in a scrolling manner alongside thepreviously received A-lines. The result is an M mode image as shown inFIG. 3 where the opposite sides of the heart chamber are most greatlyseparated when the fetal heart is relaxed at the end diastole point inthe heart cycle as indicated by arrow 42. The opposite walls of theheart chamber are in closest proximity at the peak systole phase of theheart cycle as indicated by arrow 44. FIG. 3 illustrates this cyclicalpattern of the movement of the heart wall as the fetal heart contractsand expands with each heartbeat. By tracking the changing position(motion) of the heart wall 12 or 14, a waveform in phase with the heartcycle HC can be produced. The waveform is further measured to determinethe heart rate, e.g., by measuring from peak-to-peak (or valley tovalley) periodicity of successive waves.

FIG. 4 illustrates an ultrasound display generated in accordance withone embodiment of the present invention. As shown, an ROI is identifiedin ultrasound image 48 by ROI icon 50, which has been positioned over afetal heart as shown in ultrasound image 48. Spatially different M-modelines identified as M-mode lines A, B, C and D are arranged in the ROIicon 50. In this example, the M-mode lines are arranged radially to spandiameters of the circular ROI icon, which is positioned over the fetalheart. As described further herein, the echo data corresponding toM-mode lines A, B, C and D is acquired and analyzed to identify a fetalheart beat and to measure the fetal heart rate. Here, for example, panelA′ shows that the echo data for M-mode line A registered a fetal heartrate of 158 beats per minute and panel B′ shows that the echo data forM-mode line B registered a fetal heart rate of 161 beats per minute.Panels C′ and D′ show that the M-mode lines C and D did not register afetal heart rate. The images in the panels A′ and B′ include arepresentation of movement of the fetal heart as registered from M-modeimage acquisition.

For measuring heart rate, the M-mode displays in panels A′ and B′ areanalyzed for pulsatile motion. A waveform in an M-mode scan representsthe movement of the beating fetal heart as described in FIG. 3. As shownin panels A′ and B′, a white measuring line can be used to measure timebetween individual heart cycles. In one example, by pressing a freezebutton in the system, a user can use a caliper function to measure thefetal heart cycle, in which the graphics generator 36 displays the whitemeasuring line to measure time between individual heartbeats. This canbe done by measuring from peak-to-peak (or valley to valley) of twosubsequent waves. Using the heart rate analyzer 34, a softwarecalculation can turn a measurement of the duration of a heart cycle HCinto a calculated fetal heart rate by processing data from the M-modeprocessor 30 and/or M-mode synthesizer 40 or by accessing data from theimage memory 28.

In an implementation of the present invention, a sonographer views thefetal heart and the mother's uterus in real-time using B-mode imaging.The B-mode images can, in some embodiments, be stored in a cine loop forlater analysis to determine the fetal heart rate. Concurrently orseparately, the sonographer can generate the echo data necessary tomeasure the fetal heart beat using M-mode and/or B-mode imageacquisitions. FIG. 5 illustrates an embodiment using a curved lineararray transducer 70′ having 128 scan lines to image and analyze thefetal heart 92 in a mother's uterus 94 (fetus not shown). The areascanned by the transducer for a B-mode image spans from scanline 1 toscanline 128, with scanline 64 in the middle. Preferably, repetitiveB-mode image acquisition over the 128 scan lines generates real-timeimages for the sonographer to use for positioning an ROI icon 90 aroundthe fetal heart 92. M-mode lines that span the circular ROI iconcorrespond to beams from the array transducer that can be generated withor without beam steering. As shown, beam line 1′, 64′ and 128′ are usedto generate M-mode images corresponding to three of the M-mode linesassociated with the ROI icon. The horizontal M-mode line 96 issynthesized using B-mode echo signals that are produced during B-imageacquisition. As represented by the bracket in FIG. 5, beams from scanlines 50′ through 76′ of the array transducer are used to generate echosignals from positions along the horizontal M-line 96 to produce asynthesized M-mode image.

M-mode image acquisition and B-mode image acquisition can be performedin various sequences to produce both M-mode images (normal orsynthesized) as well as B-mode images for real-time imaging by thesonographer. As shown, M-mode image echo signals are acquired alongbeams 1′, 64′ and 128′ to produce echo data associated with thecorresponding M-mode lines on the display. The echo signals used tosynthesize the horizontal M-line are collected next by scanning beams50′-76′. Echo signals from beams 1-3 are acquired and used in generateda B-mode image for display to the sonographer. This sequence of dataacquisition can proceed until a 128 scanline B-mode image is produced,during which echo data is acquired from the M-line locations multipletimes, at a much higher M-line scan rate than the B-mode frame rate. Theprocess is then repeated. Alternative sequences can also be used. Forexample, the B-mode image could be acquired in the first portion of ascan, followed by full collection of echo data for beams 1′, 64′, and128′ and then the synthesized B-mode echo signals for beams 50′-76′.

Depending on the positioning of the M-mode lines in the ROI, at leastone of the imaging lines may extend through the left ventricle (LV) ofthe fetal heart. When positioned in this manner, the imaging beam (64′in this example) will pass through the myocardial wall on one side ofthe fetal heart, through the chamber of the LV, and through themyocardial tissue on the other side of the heart. In M-mode imageacquisition, the result is an M mode image as shown in panels A′ and B′of FIG. 4 where the opposite sides of the heart chamber are most greatlyseparated where a cyclical pattern of the movement of the heart wall asthe fetal heart contracts and expands with each heartbeat can berecorded.

FIGS. 6A and 6B illustrate another embodiment of collecting echo datacorresponding to M-mode lines associated with an ROI of an ultrasoundimage. A curved linear array transducer 70′ is used to collect echosignals associated with M-mode lines associated with the ROI in theultrasound image. As shown in FIG. 6A, a grid pattern is used for theROI icon 90 that is positioned over the fetal heart 92 in the mother'suterus 94. The M-mode lines in the grid pattern correspond to M-modeimaging beams 60′, 63′, 66′ and 69′ that propagate in parallel throughthe ROI in the image. Echo data corresponding to the horizontal M-modelines h1-h5 can be acquired using echo signals generated by beams57′-72′, which are not shown in FIG. 6A for clarity. As shown in FIG.6B, echo signals at specific time points along beams 57′-72′ areacquired and used to synthesize M-mode images for the horizontal M-modelines h1-h5. As shown by the black dots in FIG. 6B, echo signals alongbeams 57′-72′ are acquired at time 1, time 2, time 3, time 4, and time 5along the beams used to generate the horizontal M-mode lines.Furthermore, the acquisition of the data can be collected using varioussequences. Here, echo signals are acquired first along beams 60′, 63′,66, and 69′ for four normal M-mode displays. Echo signals are thencollected from beams 57′-72′ for synthesizing the M-mode images of thehorizontal M-lines. Echo signals for B-mode image display to thesonographer can be collected along beams at intervals of three (e.g.,for scan lines 1, 2, and 3, followed later by 4, 5, and 6, and so on).Alternative sequences can be used. For example, the B-mode image couldbe acquired in the first portion of a scan, followed by full collectionof the M-mode images for beams 60′, 63′, 66, and 69′ and then thesynthesized B-mode echo signals for beams 57′-76′.

What is claimed is:
 1. An ultrasonic diagnostic imaging system foridentifying a fetal heartbeat, the system comprising: an ultrasoundprobe including an array transducer; an image processor adapted toprocess echo data from the probe for display; an image display coupledto the image processor and adapted to display an ultrasound imageincluding a fetal heart; and a user control adapted to initiategeneration of a plurality of spatially different M-mode lines associatedwith a region of interest in the ultrasound image, wherein the imagingsystem is adapted to: acquire echo data corresponding to the spatiallydifferent M-mode lines; analyze the echo data to measure fetal heartrates from the spatially different M-mode lines; rank the echo data ofthe spatially different M-mode lines based on the measured fetal heartrates; and identify, using the ranked echo data, the fetal heartbeatassociated with at least one of the spatially different M-mode lines. 2.The system of claim 1, wherein the system is further adapted to measurea fetal heart rate from the echo data corresponding to the M-mode lines.3. The system of claim 1, wherein at least some of the spatiallydifferent M-mode lines are automatically generated by the system.
 4. Thesystem of claim 1, wherein at least some of the spatially differentM-mode lines are generated by the system as directed by a user.
 5. Thesystem of claim 1, wherein the system is adapted to acquire the echodata corresponding to at least some of the spatially different M-modelines using M-mode or B-mode image acquisition.
 6. The system of claim1, wherein the system is adapted to synthesize echo data correspondingto at least some of the spatially different M-mode lines by combiningecho signals from a plurality of B-mode image lines produced by thearray transducer that intersect a given M-mode line.
 7. A method ofusing ultrasound imaging to identify a fetal heartbeat, the methodcomprising: receiving an ultrasound image including a fetal heart;identifying a region of interest (ROI) in the ultrasound image;generating a plurality of spatially different M-mode lines associatedwith the region of interest; acquiring echo data corresponding to thespatially different M-mode lines; analyzing the echo data to measurefetal heart rates from the spatially different M-mode lines; ranking theecho data of the spatially different M-mode lines based on the measuredfetal heart rates; and identifying, using the ranked echo data, a fetalheartbeat associated with at least one of the spatially different M-modelines.
 8. The method of claim 7, comprising determining a fetal heartrate based on the echo data corresponding to at least one of thespatially different M-mode lines.
 9. The method of claim 7, wherein thespatially different M-mode lines are automatically generated by acomputer system, generated by the computer system as directed by a user,or a combination thereof.
 10. The method of claim 7, wherein acquiringthe echo data comprises using M-mode or B-mode image acquisition. 11.The method of claim 7, wherein the receiving comprises receiving aplurality of B-mode ultrasound images stored in a cine loop, and theacquiring comprises synthesizing echo data from the B-mode images.
 12. Acomputer system for identifying a fetal heartbeat, the computer systemcomprising instructions that when executed cause the system to: receivean ultrasound image including a fetal heart; identify a region ofinterest (ROI) in the ultrasound image; generate a plurality ofspatially different M-mode lines associated with the region of interest;acquire echo data corresponding to the spatially different M-mode lines;analyze the echo data to measure fetal heart rates in the spatiallydifferent M-mode lines; rank the echo data of the spatially differentM-mode lines based on the measured fetal heart rates; and identify,using the ranked echo data, a fetal heartbeat associated with at leastone of the spatially different M-mode lines.
 13. The computer system ofclaim 12, further comprising instructions that when executed cause thesystem to determine a fetal heart rate based on the echo datacorresponding to at least one of the spatially different M-mode lines.14. The computer system of claim 12, wherein the receive step comprisesreceiving a plurality of B-mode ultrasound images stored in a cine loop,and the acquiring comprises synthesizing echo data from the B-modeimages.